õhus olev kaalutud keskmine maksimaalne kahjulike ainete kogus, mida loetakse keevitaja tervisele kahjutuks; lubatakse lühiajalist vähest normi ületamist, the maximum average airborne concentration of a hazardous material to which healthy adult workers can be exposed during an 8-hour workday and 40-hour workweek - over a working lifetime - without experiencing significant adverse health effects